Filtering devices, for instance rotary disc filter devices, are used especially for filtering off particles from liquids.
A common rotary disc filter is disclosed, for instance, in SE-C-224 131 and the principle thereof is illustrated in FIG. 1. The rotary disc filter 1 comprises a rotor having a horizontal, slowly rotating drum 11, which supports a number of parallel, disc-shaped filter members 12 which are successively arranged in spaced-apart relationship along the center axis of the drum 11 and which extend radially away from the drum (just partly shown in FIG. 1). The disc-shaped filter members 12 have, on their parallel orientated opposite lateral surfaces, openings which are covered with a filter cloth 13. Each rotary disc filter member 12 has a central opening through which a liquid A which is to be filtered can flow to the interior of the disc-shaped filter member 12. The liquid A is conducted through an inlet into the drum 11 and falls down to the interior of the disc-shaped filter members 12, from which liquid A continues to flow out through the filter cloth 13 so that the particles which are to be filtered off adhere at the inside of the filter cloth 13.
The rotary disc filter 1 can be cleaned by backwashing by means of a cleaning device of the type described, for instance, in WO 00/37159. This filter cleaning device is provided with spray nozzles 14 which are mounted on a plurality of fixed flush tubes 15, which project between the disc-shaped filter members 12. The flush tubes 15 are adapted to conduct flushing liquid to the spray nozzles 14 and are connected to an elongate liquid-conducting tube 16 which extends parallel to the centre axis of the drum 11. The spray nozzles 14 spray liquid onto the filter cloth 13 axially from outside, in a direction opposite the filtering direction and flushed-off particles are collected in a discharge duct 17 which is placed inside the drum 11 above the inlet.
U.S. Pat. No. 7,972,508 B2 discloses a rotary disc filter including a plurality of disc-shaped filter members secured about a drum. Each disc-shaped filter member has parallel orientated opposite lateral surfaces. The disc-shaped filter member is made of a plurality of modular frame members secured on the drum.
The rotary disc filter devices according to the prior art have a voluminous design. Further, the construction of the rotor is complicated or requires the expensive manufacture of specific parts. Furthermore, the rotors according to the prior art are relatively heavy in weight. In order to support such a rotor, it is necessary to provide a supporting structure having a high stability. Such a supporting structure is expensive in manufacture.
It is desirable to reduce the volume of a rotary disc filter device. It would also be desirable to reduce the cost of manufacture of a rotary disc filter device.